Grinding machine

ABSTRACT

This invention has to do with apparatus for finishing a surface of revolution by the abrasion process and includes a spindle having a roughing abrasive wheel and a finish abrasive wheel, with means for dressing them individually, with the roughing abrasive wheel being dressed more frequently than the finish abrasive wheel, with a feed mechanism by which the force between the roughing abrasive wheel and the workpiece is regulated to a predetermined value, and with an in-process gauge terminating the feeding of the roughing and finish abrasive wheels.

United States Patent Humes [54] GRINDING MACHINE [72] Inventor: Norman S. l-lumes, c/o The Heald Machine Co., New Bond St., Worcester, Mass.

[22] Filed: July 9,1970

[21] Appl. No.: 56,176

Related US. Application Data [63] Continuation of Ser. No. 686,358, Aug, 3, 1967, abandoned, which is a continuation-in-part of Ser. No. 380,780, July 7, 1964, abandoned.

[52] US. Cl ..5l/l65.88 [51] Int. ..B24b 49/18 [58] Field ofSearch..... ...51/165 R, 165.77, 165.9, 165.91,

51/165.92, 48 R, 50 R, 50 H, 103 R, 290, 291

[56] References Cited UNITED STATES PATENTS 1,949,552 3/1934 Taylor et al ..51/50 H 1,952,458 3/1934 Page ....51/50 H 2,047,041 7/1936 St. John ..5l/29O 1 Feb. 15, 1972 2,064,427 12/1936 Gurney et al. ..51/291 X 2,612,008 9/1952 Kuniholm et a1 ..51/29O X 2,647,348 8/1953 Hahn ..5l/290 X 2,961,808 11/1960 Dunigan 3,019,565 2/1962 Hatstat et al..

3,157,007 11/1964 Lockwood 3,158,965 12/1964 Lockwood et a1. ..51/l65.9l X 3,197,921 8/1965 Hohler et al. ..5 H103 R Primary ExaminerLester M. Swingle Attorney-Norman S. Blodgett [57] ABSTRACT This invention has to do with apparatus for finishing a surface of revolution by the abrasion process and includes a spindle having a roughing abrasive wheel and a finish abrasive wheel, with means for dressing them individually, with the roughing abrasive wheel being dressed more frequently than the finish abrasive wheel, with a feed mechanism by which the force between the roughing abrasive wheel and the workpiece is regulated to a predetermined value, and with an in-process gauge terminating the feeding of the roughing and finish abrasive wheels.

8 Claims, 5 Drawing Figures Pmmmrmsmz 3.641,?13

SHEET 1 (IF 3 3/ U FIG. v

WEE E Z 1 1 WHEEL: {DRESS} iDREss; I END I i l E FINISH I GRIND I g 1 FF BACKO END ROUGH GRIND BACK? 2 ND WHEEL OFF IN 5T LOAD WHEEL FIG. 2

NORMAN S. HUME S IL'VIENTUR.

PATENTEDFEB 15 I872 3.641.713

SHEET 2 GP 3 no i Ill FIG. 3

WIHEEL fi g DRESS DRESS m END FIN/SH KN GRIND END ROUGH GRIND 2 ND WHEEL IN I ST LOAD WHEEL NORMAN 5. HUME S ILWZJTORQ PATENTEOFEB 15 I972 SHEET 3 0F 3 WORKHEAD GRINDING MACHINE RELATED APPLICATIONS This application is a continuation of my application Ser. No. 686,358, filed Aug. 3, 1967, now abandoned, which in turn is a continuation-in-part of my application Ser. No. 380,780, filed July 7, 1964, now abandoned.

BACKGROUND OF THE INVENTION In the art of abrasive machining, particularly in connection with the finishing by grinding of internal bores, there has been an increased demand for accuracy of dimension and fineness of finish. Grinding machines, which have become more complex and, therefore, more expensive, have also been needed for producing a shorter cycle time; that is to say, there is a demand for a means of providing that the operation on the workpiece can be accomplished in the shortest possible time. Furthermore, because the machine represents such a large capital investment, it is required that at no time is the machine idle for any considerable period of time. In attempting to develop a machine which would not only operate rapidly on the workpiece but also give suitable dimensional characteristics and finish, a number of obstacles were encountered. In a conventional machine, there are extremely large variations in force during the grinding cycle, so that the feeding rate must be selected so that, when an extraordinarily large increase of force appears, it will not be great enough to destroy the wheel. At the same time, according to conventional grinding practice, it is necessary to dress the wheel between the roughing portion of the cycle and the finish portion of the cycle in order to obtain a proper wheel geometry and smoothness during finish. This is because the roughing portion of the cycle has a tendency to destroy the wheel geometry and surface characteristics. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide a grinding machine which is capable of producing a finish surface of excellent geometry and smoothness in a minimum amount of time.

Another object of this invention is the provision of a grinding machine capable of an extremely rapid grinding rate without sacrifice of surface quality.

A further object of the present invention is the provision of a grinding machine in which the maximum allowable force between the wheel and the workpiece may be used in grinding and in which the grinding cycle need not be interrupted for dressing before finish.

It is another object of the instant invention to provide a grinding machine making use of an extremely short grinding cycle without sacrifice of finish surface quality.

It is a further object of the invention to provide a grinding machine in which extremely high grinding forces are permissible without deterioration of workpiece surface geometry due to spindle deflection.

A still further object of this invention is the provision of a grinding machine capable of finishing workpieces at an extremely high grinding rate with a very short cycle and, yet, in which the dressing operation for the wheel may proceed at a leisurely rate without lengthening the cycle time.

Another object of the invention is a grinding machine using separate wheels for roughing and finishing in which one of the wheels can be dressed less frequently than the other.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

The character of the invention, however, may be best understood by reference to certain of its structural forms as illustrated by the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a somewhat schematic view of a grinding machine embodying the principles of the present invention,

FIG. 2 is a representation of the cycle used by the machine,

FIG. 3 is a plan view of a modification of the invention,

FIG. 4 is a representation of the cycle used in the machine of FIG. 3, and

FIG. 5 is a somewhat schematic vertical cross-sectional view of the workhead and wheelhead of the apparatus shown in FIG. 1.

SUMMARY OF THE INVENTION In general, the invention consists of a grinding machine having a base, a wheelhead mounted on the base and carrying a spindle with two spaced abrasive wheels, a workhead mounted on the base to carry a workpiece, and means bringing about relative movement between the wheelhead and the base, the said means including a feed mechanism for bringing about controlled-force grinding.

Referring to FIG. 1, it can be seen that the grinding machine, indicated generally by the reference numeral 10, consists of a base 11 on which are mounted a wheelhead l2 and a workhead 13. The wheelhead is mounted on a table 14 which, in turn, is mounted on ways 15 for movement over the base 11 in a longitudinal direction. The grinding machine is of the type shown and described in U.S. Pat. No. 3,197,921. The wheelhead 12 includes (in the preferred embodiment) an integral high-speed electric motor (not shown) which serves to drive a spindle 16. On the spindle at spaced points are mounted two abrasive wheels 17 and 18. The wheel 17 is closest to the wheelhead 12 and is of an abrasive nature particularly suited to the finishing of metallic surfaces in contrast to roughing operations. The wheel 18, on the other hand, is particularly suited for roughing grinding. For the purpose of illustrating the invention more clearly, the distances between the wheels 17 and '18 and between the wheel 17 and the wheelhead have been somewhat exaggerated; in practice, however, a spindle 16 would be made of as large a diameter as is consistent with adequate wheel life and the distances between the wheels themselves and between the wheels and the wheelhead would be made as small as possible, all of factors acting to reduce inaccuracy of the geometry of the finished workpiece surface. The workhead 13 is shown supporting a workpiece l9 and consists of the outer race of a tapered roller bearing having a conical bore 21 and a cylindrical outside surface 22, the bore 21 being the surface which is to be finished in accordance with the present invention. The workhead is provided with supporting shoes 23 which contact and support the cylindrical outer surface 22 of the workpiece. The end surface of the workpiece is contacted and rotated by a drive platen 24 suitably mounted for rotation in the workhead and driven by an electric motor 25. The workhead l3 and associated apparatus are mounted on a table 26. This table is mounted for a transverse motion on ways 27 mounted on the upper surface of a table 28. The table 28 is also mounted for transverse movement on ways 29 mounted on the upper surface of the base 11. Mounted on the front of the base is a compensation mechanism 31 which is connected by a screw 32 to a nut 33 fastened to the under side of the table 28. The compensation mechanism is intended to move the table 28 forwardly by a fixed amount at the time of each dressing cycle, as is the usual practice in the grinding art.

Connecting the table 26 and the table 28 is a feed mechanism 34 consisting of a piston 35 mounted on the table 28 and a cylinder 36 mounted on the table 26. A passage 37 extends axially through the piston 35 into the interior of the cylinder and the outboard end of this passage is connected by a conduit 38 to a source of regulated oil pressure (not shown). Mounted on the top surface of the table 26 is a dresser 39 having a diamond 41, the diamond being located between the wheelhead 12 and the workhead 13 to dress the wheels 17 and 18. Also mounted on and associated with the workhead 13 is a gauge 42 from which extends an air conduit 43. The gauge is of the pneumatic type and has a general cross section of a crescent. Its outer surface is tapered in the same general configuration as the tapered bore 21 in the workpiece and has at least one air nozzle facing toward the surface of the bore; the inner surface of the gauge is generally cylindrical and of approximately the same radius of curvature as the wheels 17 and 18. The gauge, therefore, is able to fit very closely into the space between the wheels 17 and 18 and the surface of the bore 21 in the workpiece, thus providing the largest cross-sectional area of gauge and, therefore, the most effective gauging operation. The operation of the invention will now be readily understood in view of the above description. Let us assume that a new workpiece 19 has been inserted in the workhead 13 by a conventional loading mechanism associated with the workhead. The workpiece is rotated about the axis of the bore 21 by means of the platen 24 which, in turn, is driven by the motor 25. The workpiece is located and supported in the radial direction by the support shoes 23. The spindle 16 with its wheels 17 and 18 is rotated by the wheelhead 12. The relative speed of rotation of the wheels 17 and 18 and of the workpiece 19 is selected so that their surface speeds have the conventional relationship to one another; that is to say, they rotate in the same direction and the peripheral speed of the surface of the workpiece bore is substantially less than the surface speed of the wheel. While the new workpiece is being loaded into the machine, the wheelhead 12 is at the right-hand end of the ways and the wheels 17 and 18 are entirely removed from the workpiece. At the beginning of the cycle, the wheelhead table 14 is advanced to the left along the ways 15 to make the wheel 18 coextensive with the bore 21 in the workpiece. The longitudinal motion of the wheelhead is then stopped (except for the usual longitudinal reciprocation) and oil under pressure is introduced into the conduit 38 so that the pressure oil introduced through the passage 37 into the cylinder 36 forces the table 26 forwardly relative to the table 28. The workpiece 19, therefore, advances toward the wheel 18 at a rapid rate, this rate being determined by the flow of oil into the cylinder. Once the wheel 18 strikes the surface of the bore, however, the transverse movement of the workpiece slows down to an amount determined by the spring in the spindle 16 and the pressure of the oil in the cylinder 36. Feed takes place in this way and the grinding occurs under the so-called controlled force conditions, the force between the wheel and the workpiece remaining at a constant maximum predetermined value, while the rate of movement of the workpiece transversely toward the wheel may vary from time to time in accordance with the amount of stock removal. The force which is used is selected to be somewhat below the ultimate force which can be withstood safely by the wheel 18. Grinding takes place in this manner by means of the wheel 18 until the in-process gauge 42 indicates that the bore 21 has reached a predetermined first size. At that time, the oil is released from the feed mechanism, the workpiece is retracted transversely from the wheel a short distance. Then the wheelhead moves longitudinally to bring the wheel 17 into coextensive relationship with the bore 21. Finally, oil is fed into the feed mechanism again through the conduit 38; however, in the preferred embodiment, the oil pressure is now much less, so that, when the wheel 17 begins the abrasive operation on the surface 21, the force between the wheel and the workpiece is at a much lower value than was true during the roughing portion of the cycle. This last finish" portion of the cycle takes place until the gauge 42 indicates to the control for the grinding machine that the bore 21 has reached its final desired size. At that time, the workpiece is moved rearwardly away from the spindle 16 by means ofthe feed mechanism and the wheelhead is moved longitudinally out of the bore. As the wheelhead moves to the right, carrying the spindle l6 and the wheels 17 and 18 with it, the wheels are brought into dressing engagement with the diamond 41 of the dresser 39. The surfaces of the wheels 17 and 18 are, therefore, dressed in the usual way. While this is going on, the loading mechanism associated with the workhead is removing the finished workpiece 19 from the workhead and replacing it with a new unfinished workpiece. A leisurely dressing of the wheels 17 and 18 to restore their perfect cylindrical shape and their clean surface (which elements have been affected, of course, by the previous grinding operation) may take place in a leisurely manner during the period of time required to replace the workpiece. Some time before or after the grinding cycle the compensation mechanism 31 is actuated; it revolves the screw 32 so that it cooperates with the nut 33 to draw the table 28 forwardly. This carries the table 26 and the workhead 13 with it. The amount of forward movement for this compensation is selected to make up for the fact that a ceriain amount of the diameter of the wheel has been removed during the dressing operation, as is the usual practice. Because the grinding operation takes place under controlled force conditions and because the progress of the transverse movement is regulated by the in-process gauge (rather than limit switches or the like), it is not necessary that the two wheels be the same diameter. Therefore, it is possible to dress the finish wheel 17 much less frequently than the roughing wheel 18.

It can be seen, then, that, by practicing the present invention, the maximum possible grinding force may be used without destruction of the wheel. At the same time, it is not necessary to reserve a long period of time in the cycle between the roughing portion of the cycle and the finish portion of the cycle for dressing the abrasive wheel. Nevertheless, the finished product is perfect both in geometry and finish because the wheel which is brought into play for the finishing portion of the cycle is in excellent condition. The fact that the wheel which is used in the roughing portion of the cycle has had its geometry and surface smoothness destroyed by the agressive high force grinding operation does not affect the quality of the product after the finish portion of the cycle has been completed.

FIG. 2 shows diagrammatically the movement of the apparatus shown in FIG. 1 through a typical cycle. The diagram is drawn as though the workpiece remains fixed in space and the sole movement takes place by movement of the wheel. The path shown in the diagram is the path moved by the wheel with the workpiece remaining fixed; as applied to the sort of machine shown in FIG. 1 (wherein the wheel does all the longitudinal movement and the workpiece does all the transverse movement), the line shows the relative movement between the parts. In any case, assuming that the wheel does all the moving, the wheel is located at the right at the spot labeled load at the beginning of the cycle. When loading has been completed, the wheel moves to the left to the point labeled FIRST WHEEL IN. At this point the roughing wheel 18 lies within the workpiece and longitudinal movement stops (except for short, rapid reciprocation). The feeding then takes place transversely and the wheel moves toward the workpiece surface through the air until it strikes the workpiece surface and then cuts into the workpiece surface until the point labeled END of ROUGH GRIND takes place. This point is determined by the gauge which sends an air signal to the main control of the machine. The wheel then moves transversely away from the workpiece to the point labeled BACKOFF. At that time, the wheel begins a longitudinal movement relative to the workpiece until the point is reached at which the second wheel (which is the finish wheel 17) lies within the workpiece. At that time, transverse movement takes place again with the wheel passing through the air until it reaches the workpiece surface and begins a grinding operation on the workpiece surface. Since the wheel 17 is considerably larger than the wheel 18 (as will be explained hereinafter), the wheelhead will not have far to move transversely before the finish grinding operation begins, thus saving a considerable period of time in the cycle. Eventually, as the grinding progresses, the gauge 42 will indicate that the FINISH SIZE hasbeen reached and will set the controls in motion to retract the wheel from the work. The movement of the wheel away from the workpiece will take place until the BACKOFF point is reached, at which time longitudinal movement will take place until both wheels are removed from the workpiece. Presumably, the diamond will be adjusted so that at that time during that longitudinal movement, the wheel 17 may pass by the diamond and be dressed by it very infrequently without need for further transverse movement; under certain circumstances, however, it may be necessary to move the wheels transversely to arrange for proper dressing of the wheel 17. The wheels 17 and 18 are of appreciably different diameter so that it is necessary (after the wheel 17 has passed by the diamond) to move the wheels laterally once more so that, as the wheel 18 passes by the diamond, it is dressed in a suitable manner, probably during every cycle. After the wheel 18 has passed the diamond, the wheels are moved back to the original line and returned to the right-hand position to the point labeled LOAD. From the moment that the wheel 18 is clear of the workpiece and during the dressing operation, the loading operation is being carried on so that it will be understood that, as a practical matter, the loading operation is probably close to being completed by the time the wheels reach the right-hand end and the cycle is ready to start all over again.

FIG. 3 shows a grinding machine 1 specifically adapted to grind a groove in an outer race of a ball bearing. Mounted on the base 111 is a wheelhead 112 and a workhead 113. The wheelhead 112 is mounted on a table 114 which is capable of longitudinal movement relative to the base 111 on ways 115. Extending from the wheelhead 112 is a spindle 116 carrying a relatively large finishing wheel 117 and further out on the spindle a relatively small roughing wheel 118; both wheels are of the type having a rounded annular surface for grinding grooves. A workpiece 119 is shown as consisting of the outer race of a ball bearing and has an internal annular groove 120 whose surface is to be finished. The groove opens onto a cylindrical bore 121 and the workpiece has an outer cylindrical surface 122 by which it is supported. The workhead 113 is shown as having work-supporting shoes 123 which contact the outer cylindrical surface 122 of the workpiece and supports it for rotation. The other end of the workpiece is contacted by a platen I24 driven by an electric motor 125. The workhead 113 is mounted on a table 126 which is mounted for transverse movement on ways 127; these ways are, in turn, mounted on a table 128 which also is capable of transverse movement relative to the base 111 by means of ways 129 extending from the upper surface of the base. Mounted at the front of the base is a compensation mechanism 131 which is connected to a nut 133 in the bottom of the table 128 by means of a screw 132. Extending between the rear of the table 126 and the table 128 is a feed mechanism 134 consisting of a piston 135 which is firmly attached to the table 128 and a cylinder 136 fastened to the top surface of the table 126 and in which the piston 135 resides. Oil is fed into the cylinder 136 through a passage 137 extending through the piston 135 and joined to a conduit 138 connected in the usual way to a source of pressure oil. Mounted on the table 126 and extending between the wheelhead 112 and the workhead 113 is a dresser 139 having a diamond 141. This dresser is particularly adapted to dress annular wheels.

Extending into the workpiece in the space between the wheels and the surface of the bore 121 is a gauge 142 whose operating point carries an air nozzle closely adjacent the bottom of the groove 120 with air under pressure flowing to the nozzle through a conduit 143. The gauge 142 is similar to that shown in the U.S. Pat. of Lockwood No. 3,157,007.

The operation of the apparatus will now be readily understood in view of the above description and, particularly, with reference to FIG. 4, which shows a typical grinding cycle used in grinding a groove by means of the grinding machine 110. Starting at the point labeled LOAD, the wheels reside well away from the IN in and from the dressing apparatus 139. The wheels are first advanced to the left until the roughing wheel 118 resides within the workpiece opposite the groove 121. Longitudinal motion stops at this point labeled FIRST WHEEL IN. The wheel then advances transversely into the groove, so that it eventually contacts the workpiece surface and begins the grinding operation. Grinding takes place until the gauge indicates the END ROUGH GRIND. At that time, the wheel moves transversely away from the workpiece until it clears the groove and reaches the BACKOFF point at which time the spindle is advanced further to the left until the point is reached at which the finish wheel 117 lies opposite the groove of the workpiece, this point being indicated as SECOND WHEEL in FIG. 4. The wheel is then advanced toward the workpiece until it contacts the surface of the groove and begins the final or FINISH operation. Eventually, the gauge indicates that the groove has reached the desired finish size at the point labeled END FINISH GRIND. At that time, the wheels are retracted from the workpiece until the largest wheel clears the groove 120. Then, the wheels are moved to the right until the finish wheel 117 lies exactly opposite the dresser. Longitudinal movement of the wheelhead to the right is then stopped completely and the wheel is advanced transversely of the diamond by means of the oil in the feed mechanism 134. The wheel 117 is, on infrequent occasions, advanced toward the diamond until it is in a position to be engaged by the diamond; it is stopped in that position but continues to rotate, of course. The dresser is actuated so that the diamond sweeps in a horizontal arc and cleans the surface of the wheel in the usual way. The dresser motion is stopped and the wheel is retracted and then moved to the right again until the roughing wheel 118 arrives opposite the dresser. The wheel is advanced toward the dresser again, its transverse and longitudinal motion both stopped while the wheel continuously rotates, and the dresser 139 carries the diamond 141 over the surface of the wheel to renew it in the usual way. With the dressing completed, the spindle with its wheels is moved transversely and longitudinally back to the LOAD position. After the dressing operation, the compensating mechanism 131 is operated to make up for the fact that the surface of the wheel 118 is now in a different position relative to the groove 120 in the workpiece which is to be finished. Movement of the wheel, whether it be the roughing wheel 118 or the finish wheel 117, into contact with the surface of the groove takes place under the controlled force method of feeding, so that the relative positions of the surface of the wheels is not critical. This means that the wheels can be of different sizes and means that the individual wheels may be dressed only when it is necessary. That is to say, if it is possible to omit dressing the finishing wheel 118 for a number of cycles but it is necessary to dress the roughing wheel 117 during each cycle, this may be accomplished with the machine of the present invention, even though it means that the wheels will be different sizes. As a matter of fact, if such a staggered dressing arrangement is continued for any length of time, the wheels will necessarily be of substantially different sizes but, by using the grinding machine of the present invention, this wheel size differential will not affect the finished workpiece. The result is that there will be longer wheel life and that it is possible to keep the cycles considerably shorter than otherwise.

FIG. 5 shows the details of construction of the apparatus that permits the use of two different backoff positions during the grinding cycle shown in FIG. 2 and also two different feed stops as well as different compensations for dressing the two abrasive wheels. The workhead table 26 rests on the ways 27 and carries the workhead 24. It is moved forward (to the left) by the piston 35 and rearwardly by a cylinder 44. The forward motion is terminated by an adjustable stop 45 striking an abutment 46, this bringing about the END OF FINISH GRIND. At the other side of the table, the rearward motion is terminated at a BACKOFF point after finish grind by the finish wheel 17 by the engagement of a stop 47 with a block 48; the position of the block 48 is adjusted to provide compensation after dress by a screw 49 rotated by a stepping motor 51. The wheelhead table 14 is supported on the ways 15 and is provided with an upper table 52 which actually supports the wheelhead 12. A cylinder 53 moves the table 52 forwardly and rearwardly over the table 14. The rearward motion is terminated for END OF ROUGH GRIND by the engagement ofa stop 54 with a block 55. The motion in the forward direction is terminated at BACKOFF by the engagement of a horn 56 extending downwardly from the table 52 and adapted to engage a surface of the block 55. The block is adjustable for compensation after dress by a screw 57 associated with a stepping motor 58.

It can be seen that a number of advantages accrue from using the above arrangement of parts, First of all, by using one wheel for rough grinding and another wheel for finish grinding it is not necessary to interrupt the grinding cycle to dress for the finish portion of the cycle. Furthermore, because the method of feeding is by the controlled-force method and because in process gauging is used, the relative sizes of the wheels is unimportant. This makes it possible to dress the roughing wheel as frequently as is necessary, but it is necessary to dress the finish wheel only infrequently. As a matter of fact, under some conditions (because the finish wheel is only used for finishing and sizing and because the roughing wheel is doing all of the heavy grinding) it may be possible to dress the finish wheel only when a new roughing wheel is mounted on the spindle. In other words, one finish wheel will outlast a number of rouging wheels and it is possible to dress the finish wheel only when a rough wheel is being replaced. This means that, under some circumstances, only one wheel need be dressed during the loading portion of the cycle so that even the loading portion of the cycle can be shortened considerably. This means that not only is the actual grinding tak ing place with the greatest possible grinding force but there is no interruption of this grinding for dress. Furthermore, a previous disadvantage of the use of two wheels on the same spindle has been removed; this disadvantage is that extremely long spindle is, of course, required to carry the two wheels and to permit adequate dressing of the two wheels. In the present invention, the finish wheel is closely adjacent the wheelhead and is, therefore, at the end of a short cantilever so that spindle deflection is much less of a problem during the finishing portion of the cycle. The rouging wheel is on the outer end of the spindle and, of course, is subject to more deflection, but this deflection occurs during the roughing portion of the cycle and any deficiencies in the geometry of the bore can be corrected during the finishing portion of the cycle.

It is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

The invention having been thus described, what is claimed as new and desired to secure by Letters Patent is:

l. A grinding machine, comprising a. a base,

b. a wheelhead mounted on the base and carrying a cantilevered spindle having a roughing abrasive wheel and a finishing abrasive wheel adjacent the wheelhead,

. a workhead mounted on the base and adapted to carry a workpiece having a surface of revolution to be finished,

d. a feed mechanism for bringing about relative movement transversely of the spindle axis between the workhead and the wheelhead in such a manner that the grinding force between the roughing wheel and the workpiece is regulated to a predetermined value, e. a dresser, f. means presenting the wheels to the dresser so that the roughing wheel is dressed frequently and the finishing wheel is dressed infrequently, and

an in-process gauge terminating the feeding of the roughing and finishing wheels, so that finished size, geometry, and finish is maintained at predetermined values despite differences in wheel size.

2. A grinding machine as recited in claim 1, wherein the dresser is located between the workpiece and the wheelhead.

3. A grinding machine as recited in claim 1, wherein the means presents the wheels to the dresser at different locations transversely of the spindle axis.

4. A grinding machine as recited in claim 1, wherein a compensation mechanism is provided to produce a predetermined movement between the wheelhead and the workhead to com pensate for reduction In the diameter of the roughing wheel due to dressing.

5. A grinding machine as recited in claim 1, wherein means is provided to give different backoff positions for the two wheels after the roughing and finishing grinding operations.

6. A grinding machine as recited in claim 1, wherein means is provided for bringing about relative movement transversely and longitudinally of the spindle axis between the workhead and the wheelhead to bring about a grinding cycle, the means including a feed mechanism for producing controller-force grinding, the cycle including a longitudinal movement of the roughing wheel into the workpiece, a transverse movement to produce a roughing grind, a retraction to remove the roughing wheel away from the surface, a longitudinal movement to bring the finishing wheel into the workpiece, a transverse movement to bring about a finishing grind, a retraction to remove the finishing wheel from the surface, a longitudinal movement to remove both wheels from the workpiece, a combination of longitudinal and transverse movements to bring the roughing wheel into operative relationship to the dresser, and a combination of longitudinal and transverse movements to bring the finishing wheel into operative relationship to the dresser.

'1. A grinding machine as recited in claim 6, wherein the surface of revolution is one whose generatrices are straight lines, wherein the two abrasive wheels are of cylindrical form, wherein the dresser is fixed, and wherein the finishing wheel is dressed by moving the wheel longitudinally past the dresser along a first transverse line and the roughing wheel is dressed by moving the wheel longitudinally past the dresser along a second transverse line.

8. A grinding machine as recited in claim 6, wherein the surface of revolution is annular, wherein the two abrasive wheels are of annular form, wherein the dresser operates to move a diamond in a dressing arc, and wherein the finishing wheel is dressed by holding the wheel at a first transverse position with its surface within the dressing arc and the roughing wheel is dressed by holding the wheel at a second transverse position with its surface within the dressing arc. 

1. A grinding machine, comprising a. a base, b. a wheelhead mounted on the base and carrying a cantilevered spindle having a roughing abrasive wheel and a finishing abrasive wheel adjacent the wheelhead, c. a workhead mounted on the base and adapted to carry a workpiece having a surface of revolution to be finished, d. a feed mechanism for bringing about relative movement transversely of the spindle axis between the workhead and the wheelhead in such a manner that the grinding force between the roughing wheel and the workpiece is regulated to a predetermined value, e. a dresser, f. means presenting the wheels to the dresser so that the roughing wheel is dressed frequently and the finishing wheel is dressed infrequently, and g. an in-process gauge terminating the feeding of the roughing and finishing wheels, so that finished size, geometry, and finish is maintained at predetermined values despite differences in wheel size.
 2. A grinding machine as recited in claim 1, wherein the dresser is located between the workpiece and the wheelhead.
 3. A grinding machine as recited in claim 1, wherein the means presents the wheels to the dresser at different locations transversely of the spindle axis.
 4. A grinding machine as recited in claim 1, wherein a compensation mechanism is provided to produce a predetermined movement between the wheelhead and the workhead to compensate for reduction in the diameter of the roughing wheel due to dressing.
 5. A grinding machine as recited in claim 1, wherein means is provided to give different backoff positions for the two wheels after the roughing and finishing grinding operations.
 6. A grinding machine as recited in claim 1, wherein means is provided for bringing about relative movement transversely and longitudinally of the spindle axis between the workhead and the wheelhead to bring about a grinding cycle, the means including a feed mechanism for producing controller-force grinding, the cycle including a longitudinal movement of the roughing wheel into the workpiece, a transverse movement to produce a roughing grind, a retraction to remove the roughing wheel away from the surface, a longitudinal movement to bring the finishing wheel into the workpiece, a transverse movement to bring about a finishing grind, a retraction to remove the finishing wheel from the surface, a longitudinal movement to remove both wheels from the workpiece, a combination of longitudinal and transverse movements to bring the roughing wheel into operative relationship to the dresser, and a combination of longitudinal and transverse movements to bring the finishing wheel into operative relationship to the dresser.
 7. A grinding machine as recited in claim 6, wherein the surface of revolution is one whose generatrices are straight lines, wherein the two abrasive wheels are of cylindrical form, wherein the dresser is fixed, and wherein the finishing wheel is dressed by moving the wheel longitudinally past the dresser along a first transverse line and the roughing wheel is dressed by moving the wheel longitudinally past the dresser along a second transverse line.
 8. A grinding machine as recited in claim 6, wherein the surface of revolution is annular, wherein the two abrasive wheels are of annular form, wherein the dresser operates to move a diamond in a dressing arc, and wherein the finishing wheel is dressed by holding the wheel at a first transverse position with its surface within the dressing arc and the roughing wheel is dressed by holding the wheel at a second transverse position with its surface within the dressing arc. 